<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            background-color: yellow;
        }
        .red{
            background-color: red;
        }
        .bigger{
            width: 200px;
            height: 200px;
        }
    </style>
    <script src="jquery.3.4.1.js"></script>
</head>
<body>
<div></div>
</body>
</html>